The present invention relates to the field of remediation of chemical contamination, including for example, contamination in particulates such as soil and also in fluids such as groundwater. More particularly, the present invention relates to a method of efficiently treating particulates and fluids contaminated with organic materials, such as hydrophobic aromatic hydrocarbons using biocompatible methods for oxidation of the organic contaminants.
Chemical contamination of the environment, particularly of soil and groundwater is currently a widespread problem that is prevalent in many parts of the industrialized world. Industrial pollution has contaminated millions of acres of soil and associated aquifers. Often, cleanup of the contamination is avoided because of the costs of remediation, and the land may remain unused or abandoned.
Typical remediation (decontamination) strategies include incineration and/or removal. In the case of contamination of large areas, an on-site incinerator may be warranted. In other cases, generally on a smaller scale, excavation and removal to an RCRA (Resource Conservation and Recovery Act) compliant incinerator or landfill may be employed. Both of these methods require intensive labor and mechanical effort resulting in high costs. Other methods in frequent use include pumping and treating, vacuum extraction, steam flooding, air sparging and soil flushing.
Treatment of contaminated soils in situ by various methods has been pursued because it does not require excavation or hauling and is less costly. Oxidation is one technique used to treat contaminated soils in situ. For example, one such oxidation technique that has been widely used is oxidation of organic compounds with ozone, potassium permanganate or hydrogen peroxide.
Additionally, efforts have been made to reduce the costs of treatment with chemicals by more effectively directing the chemicals used in the treatment to the contaminated soil to the appropriate location and depth. For example, U.S. Pat. No. 5,525,008 to Wilson discloses a method of directing the flow of the oxidizing treatment solutions to contaminants in the soil or groundwater. The invention discloses the use of multiple horizontally spaced sealed injection wells, with the goal of directing the reactive solution through the contaminated area.
Another approach at directing treatment chemicals to the contaminates in soil is disclosed by U.S. Pat. No. 4,591,443 to Brown. The ""443 patent discloses a method of decontaminating subterranean soil by controlling the mobility of aqueous treatment fluids. In order to direct the treatment fluid containing the active chemical, such as hydrogen peroxide to the intended reaction site, hydratable polymers are used as viscosity modifiers. Optionally, cross linking agents may be added to further increase the viscosity of the treatment fluid. Surfactants are employed to decrease the interaction of metals or clays with peroxide. The ""443 patent further discloses the use of peroxide stabilizers, free radical initiators such as iron (Fe) and also free radical inhibitors. Penetrating pre-treatment fluids for altering the reactivity of the soil or rock formation and inactivating hydrogen peroxide decomposition catalysts are also disclosed.
The ""443 patent teaches that these various oxidation and flow modifiers combine to provide a degree of spatial and temporal control of the oxidizing treatment chemicals, with the stated intention of reacting with the desired chemical contaminants rather than the surrounding naturally occurring minerals and soil. The ""443 patent does not address the use of bioremediation, to treat many common forms of contamination, particularly organic contaminants such as polycyclic aromatic hydrocarbons (PAHs), thereby permitting reduced chemical exposure and loading of the site. The ""443 method would be expected to produce poor oxidation of, e.g. anthracene and chrysene, and other such hydrocarbons.
Bioremediation has begun to gain wider acceptance as a viable treatment technology for remediating soils, sediments and subsurface sites contaminated with hydrocarbons. The attractiveness of bioremediation arises at least in part from the fact that the process takes advantage of intrinsic biodegradative processes of microorganisms and because the compounds that are the target of remediation are degraded to innocuous end products. In this respect, bioremediation-based remediation approaches using either in situ or off site designs have been successfully employed for remediation of soils and subsurface sites contaminated with lighter fractions of petroleum or petroleum products, and for the lower molecular weight and more water soluble aromatic components of petroleum products, represented, for example, by benzene, toluene, ethylbenzene and xylenes.
Bioremediation strategies, however, often have limited applicability when soils, sediments and subsurface sites are contaminated with complex mixtures of highly hydrophobic aromatic compounds such as commonly occurs for instance with tar residues. The polycyclic aromatic hydrocarbons (PAHs) that are component of tar residuals, remain a challenge for the application of in situ remediation strategies owing to the low aqueous solubility of mixed PAH components. Such PAHs are produced, for example, from the volatile components of bituminous coals in coal carbonization, from the residue of gasifying oils in oil gas processes, and from the cracking of enriching oils in carbureted water gas production at former manufactured gas plant (MGP) sites. Bioremediation of such PAH-contaminated sites is hampered by the low aqueous solubility of PAH compounds, which leads to low bioavailability where the compounds are not available for microbial action that depends on aqueous chemistry and enzyme action.
Hydrogen peroxide, in the presence of ferrous ions (Fe++) as a catalyst, generates a strong nonspecific oxidant hydroxyl radical that reacts with most organic compounds at diffusion-controlled rates of 107 to 1010 Mxe2x88x921 sectxe2x88x922. This is known as Fenton""s reaction and has been used for the destruction of organic contaminants including (poly)chlorinated aromatic compounds and a variety of herbicides in aqueous solutions or soils. However, little evidence is available regarding whether the Fenton""s reaction can mineralize organic contaminants, or whether the resulting partially oxidized organic compounds pose less hazards than the parent compounds. Moreover, use of Fenton""s reaction produces soil pH changes which are incompatible with bacteria and make subsequent use of bioremediation methods ineffective.
Although Fenton""s reagent has the potential to non-specifically oxidize many PAHs, it also results in a substantial lowering of the soil pH, e.g. to a pH of between 2 and 3. At these pH levels, many heavy metal contaminates become solubilized and migrate into ground water. Moreover, this pH range is subsequently incompatible with many forms of biological treatment.
As noted above, one serious disadvantage of the use of chemical oxidation with bioremediation is the lowering of soil pH to levels which solubilize many heavy metals and which are unacceptable for sustaining many useful bacteria. Nonetheless, various attempts at treating contaminated soils have included a combination of bioremediation and chemical treatment.
U.S. Pat. No. 5,955,350 to Soni et al. discloses the stepwise use of biological treatment, then chemical treatment followed by another biological treatment of organic waste. Hydrogen peroxide is a strong oxidant and is very reactive. The ""350 patent discloses the use of Fenton""s reagent and peroxide between two stages of biological remediation.
One severe drawback of the use of Fenton""s reagent is that in some circumstances, the rapid reaction of peroxide can result in excessive heat and consequent generation of steam, creating high pressures and potentially resulting in an explosive release. In the field, various approaches to the problem of explosive potential are used. These include adaptations such as venting the formation or utilizing a slow introduction of the peroxide. The ""350 patent discloses a slow rate of addition of peroxide in order to avoid high rates of oxidation. Manageable temperatures are maintained by slow addition of hydrogen peroxide, exemplified by the addition of an approximate rate of 1 to 100 mg hydrogen peroxide per hour per gram of contaminated soil to the ferrous salt solution.
U.S. Pat. No. 5,610,065 to Kelley et al. also discloses combined chemical and biological remediation including the use of Fenton""s reagent for degradation of high molecular weight PAHs in soil. The ""065 patent is silent as to pH control during the oxidation process. It is not surprising, therefore, that the ""065 patent follows chemical oxidation with additional microbial inoculation in an effort to restock the microorganism population after exposure to the harsh oxidation conditions. The ""065 patent also discloses the use of a lower alcohol to increase the aqueous solubility of PAHs.
U.S. Pat. No. 5,741,427 to Watts utilizes stabilizers to provide chemical ligands for Fe(III) species during Fenton""s oxidation. The stabilizer ligands are provided by phosphates, silicates, or citrates. Control of pH is not addressed. Similarly, the aforementioned problems associated with oxidation of soil contaminants are not addressed.
To date the known methods which employ oxidation and/or bioremediation techniques to treat contaminated soils all suffer from the various disadvantages discussed above. It would therefore be desirable to provide a means by which oxidation of contaminates can occur efficiently without the need for undesirable changes in pH. There is a need for a remediation method that is operational in a neutral pH range with increased biocompatibility and that reduces the solubilization of heavy metals. It would also be desirable to provide a treatment method which avoids further contamination due to the formation of unwanted or toxic by-products as a result of the treatment.
The invention provides a method of treatment of a contaminated material, herein referred to as a contaminate, contaminated with an organic compound. The method includes the steps of: providing a contaminate that is contaminated with an organic compound, and treating the contaminate with a chemical oxidation step. The chemical oxidation step includes: contacting the contaminate with a transition metal in soluble form; and a chelator of the transition metal, (such that the chelator of the transition metal and the transition metal form a transition metal:chelator complex); and an oxidizing agent that provides a reactive free radical in the presence of the transition metal complex; and a buffering salt to maintain the pH in the neutral range. The method provides a reactive free radical that initiates a chemical reaction with the organic compound to produce reaction products of the organic compound.
The method of treatment may further include pre-treating the contaminate with a biodegradation step prior to or after the chemical oxidation step. The biodegradation step includes a step of contacting the contaminate with a microbial consortium under conditions suitable for the consortium to mediate solubilization or biodegradion of the organic compound.
The invention also provides a kit for treatment of a contaminate contaminated with an organic compound, the kit comprising: (i) a transition metal in soluble form; (ii) a chelator of the transition metal that has the property of forming a transition metal:chelator complex with the transition metal; and (iii) and a buffering salt to maintain the pH in the neutral range. The kit may further comprise a microbial consortium having the property of solubilizing or biodegrading an organic compound contaminant.
The invention further provides a method of producing a reactive free radical in an aqueous medium in a neutral pH range, by providing a transition metal in soluble form in an aqueous medium, along with a chelator of the transition metal, such that the chelator of the transition metal and the transition metal form a transition metal:chelator complex; a buffering salt is optionally included to maintain the pH in a neutral range with an oxidizing agent that provides a reactive free radical in the presence of the transition metal:chelator complex.
The present inventors have discovered methods that are safer, more effective and less expensive than the known methods for degrading organic contaminants present in particulate materials or in liquid wastes. The methods are also effective for the degradation of pollutants, the reduction of toxicity, the reduction of chemical or biological oxygen demand and the removal of odors or color of a contaminate. The method involves oxidation of the contaminant compounds by chemical treatment with optional biodegradation steps. These methods are particularly effective in remediating organic contaminants, especially hydrocarbons that may have low solubility and low bioavailability. Such contaminants are poorly if at all transformed by natural processes alone.
Particulate materials such as soils and solid waste materials include for instance, gravel, pebbles, stone, stone chips, rock, ore, mining waste, coal, coke, slag, concrete, brick, construction material, demolition material, vermiculite, synthetic resin or plastic. Liquid wastes, include for example, industrial effluents in pools or holding ponds, contaminated ground water, liquid sludge as well as less polluted aqueous run off. Such contaminated particulates, solids and liquids, are hereinafter interchangeably referred to as contaminates. Preferably the contaminate is soil or ground water.
As used in the present specification the term xe2x80x9ccontaminatexe2x80x9d refers to any matter containing an undesirable chemical component or pollutant. Examples of such undesirable chemical components or pollutants include, for instance, toxic chemicals, carcinogens, organic compounds, polycyclic compounds, aromatic compounds, aliphatic compounds, olefinic compounds, ethynic compounds, acids, bases, alcohols, dyes, oils and the like.
Among the contaminants that may be addressed by the methods of the present invention are the following listed for exemplification only and are in no way to be considered as limiting: hydrocarbons, polyaromatic hydrocarbons (PAHs); dense non-aqueous phase liquids (DNAPLs) and light non-aqueous phase liquids (LNAPLs); solvents, particularly chlorinated solvents; tars and creosote; petroleum products and byproducts such as: any one or combination of the followingxe2x80x94benzene, toluene, ethyl benzene and xylene (known as BTEX), PAH, TPH and diesel fuel; chlorinated hydrocarbons such as vinyl chloride, trichloroethylene (TCE), tetrachloroethylene, TCA, DCA, PCA and PCBs; chlorinated dioxins and dibenzofurans; phenolics; preservatives; pesticides; explosives and unspent munitions.
As used in the present specification the term xe2x80x9cthe neutral rangexe2x80x9d used in reference to a pH range refers to a pH in a range around the neutral pH, which is pH of about 7. Preferably the pH is in a range from about pH 5 to about pH 8. More preferably the neutral pH range is from about pH 5.5 to about pH 7. Optimally the neutral pH range as referred to herein is from about 6 to about 6.5.
As used herein the term xe2x80x9cbuffering saltxe2x80x9d means any salt maintains the pH in the neutral range. Preferably the buffering salt is soluble in acidic solution. The buffering salt may have a pKa in the range of about 5 to about 8. A preferred buffering salt is calcium carbonate (CaCO3).
In one aspect the present invention provides a method of treatment of organic compounds in a contaminate using a chemical oxidation process. The treatment is effective for remediation of water-insoluble, toxic, carcinogenic and environmentally persistent organic compounds, particularly those with a bioavailability too low for effective use of direct bioremediation methods.
The chemical oxidation treatment of the present invention is mediated by a reactive free radical, that may be an oxidizing free radical produced by the action of a transition metal ion on an oxidizing agent at a pH in the neutral range. The oxidizing free radical may be any oxidizing free radical produced by the action of a transition metal ion on an oxidizing agent, such as for example the oxidizing free radicals .OH or .OOH, produced by the action of a transition metal ion:chelator complex on hydrogen peroxide.
The transition metal ion is stabilized by a metal chelator and the pH is maintained by the addition of a buffering salt. The reactive free radical initiates a chemical reaction with the organic compound contaminants that results in remediation of the contamination, such that the organic compounds are remediated. Preferably, remediation of the organic contaminants results in one or more of the following: the organic compound is solubilized, rendered more bioavailable, oxidized, degraded, decomposed, detoxified or mineralized.
In another aspect of the invention there is provided a method which combines oxidation and bioremediation of contaminants and which provides a means to control the pH to provide an environment suitable for chemical and biological transformations by microorganisms. Suitable microorganisms include any microorganism capable of oxidation of a contaminant, especially such microorganisms as bacteria, actinomycetes and fungi. A suitable microorganism may be used as a single microbial species. Preferably, however, the microorganisms exist as a population of two or more species, which may be of different genera. Such a population of two or more suitable microorganisms is a herein referred to as a consortium. Yet more preferably, the consortium performs its natural degradative processes on the contaminants.
In yet another aspect the invention provides a method for decontaminating or remediating contaminated soil and water by providing to a soil a consortium of microorganisms, selected to degrade known contaminants which may be present in the soil, and allowing the microorganisms to degrade the contaminants in situ. Additionally, the soil remediation provided by the selected consortium may be further enhanced by introducing chemical oxidation treatment, prior to, simultaneously with or subsequent to the introduction of the microbial consortium. The oxidation is desirably carried out while maintaining a biocompatible pH to permit the consortium to degrade the contaminants. Preferably, the consortium is capable of this transformation as a natural degradation process, though selection may be applied to the consortium to enhance the degradative activity.
A particular advantage of the methods taught herein is that these methods are compatible with the biological degradative processes mediated by the microorganisms introduced as microbial consortia, though the introduction of single species of microorganisms to perform this function is also contemplated. The degradative processes mediated by the microorganisms or consortia may be natural processes of the microorganisms.
Microorganisms present in a preferred consortium useful in the methods of the present invention include Sphingomonas yanoikuyae, Sphingomonas species., and Pseudomonas species. In another preferred consortium the microorganisms include Burkholderia species, Ochrobactrum species, and Actinomyces species.
Other useful microorganisms in the methods of the present invention that involve bioremediation include: Pseudomonas aeruginosa (ATCC 15522-28, 21472); Pseudomonas species (NRRL 18064); Alcaligenes faecalis (ATCC 8750); Alcaligenes eutrophus (NRRL 15940); Rhodotorula rubra (ATCC 16639); Rhodococcus globerulus (NRRL 55255), and Xanthomonas maltophilia (ATCC 25556).
The microorganisms may be delivered by any one of the many well known methods. Examples include for instance, those described in the following references which are not to be construed as limiting in any way:
Newcombe, D. A., and D. E. Crowley. 1999. Bioremediation of atrazine-contaminated soil by repeated applications of atrazine-degrading bacteria. Appl Microbiol Biotechnol. 51(6):877-82.
Barbeau, C, L. Deschenes, D. Karamanev, Y. Comeau, and R. Samson. 1997. Bioremediation of pentachlorophenol-contaminated soil by bioaugmentation using activated soil. Appl Microbiol Biotechnol. 48(6):745-52.
The inventors have discovered a method of oxidation of hydrocarbon contaminants in situ that is biocompatible. This biocompatibility means that microorganisms may be employed at any of the various stages of the method. This method therefore allows combined chemical oxidation treatments with biodegradation steps with a microbiological culture or consortium. The microbiological treatments steps bring the advantages of microbiological remediation to the treatment methods of the present invention. These advantages include low environmental impact, low cost of the microbiological culture or consortium, mild conditions of use and ease of application of the microbiological culture or consortium to the contaminate before, during or after the chemical remediation treatment steps as taught herein.
The inventors further provide a generally useful method of producing a reactive free radical under very mild conditions in an aqueous medium at a neutral pH. The method essentially includes providing a transition metal in aqueous soluble form, along with a chelator of the transition metal, to form a transition metal:chelator complex; a buffering salt may be included to maintain the pH in a neutral range and an oxidizing agent is added to provide the reactive free radical in the presence of the transition metal:chelator complex. Such complexes are interchangeably referred to as transition metal:chelator complexes or chelates in this specification.
The standard Fenton""s reaction involves the production of a hydroxyl radical by the action of ferrous ions on hydrogen peroxide, to release a ferric ion and a hydroxyl ion along with the hydroxyl radical. The ferric ion then catalyses the production of an oxyhydroxyl radical and a hydrogen ion from the hydrogen peroxide and reforms the ferrous ion. This reaction is carried out at low pH. The hydrogen peroxide is introduced slowly to avoid explosive decomposition to oxygen catalyzed by the transition metal, which is in this case, iron.
In the methods of the present invention, a buffering salt is added to maintain the acidity at a neutral or near neutral pH. The transition metal is further stabilized by the binding of the chelating agent. These modifications prevents the precipitation of the transition metal as an insoluble salt and further renders the entire process more biocompatible. The bioavalable degradation products may then be further degraded by any added microbial culture or consortium that is introduced.
Addition of reagents may be in any order and as transition metal chelates or separately such that the chelates form in situ. In the case where the transition metal salt is a ferrous or ferric salt, the chelating agent stabilizes the ferric form and prevents precipitation of the ferric salts particularly ferric hydroxide.
Reaction times vary with the prevailing conditions, such as temperature, contaminant organic compound and reagent (transition metal ion, chelating agent and hydrogen peroxide) concentrations. Significant degradation may occur over several days, though reaction times of less than 1-2 days are preferred and reaction times of 24 hours or less are optimally preferred.
Delivery of the chemical reagents for the method of the present invention may be achieved by any of a variety of methods well known and set forth in the art. These include for example the methods described in the following references:
Watts, R. J., D. R. Haller, A. P. Jones, and A. L. Teel. 2000. A foundation for the risk-based treatment of gasoline-contaminated soils using modified Fenton""s reactions. J Hazard Mater. 76(1):73-89.
Kao, C. M., and M. J. Wu. 2000. Enhanced TCDD degradation by Fenton""s reagent preoxidation. J Hazard Mater. 74(3):197-211.
Arienzo. M. 2000. Use of abiotic oxidative-reductive technologies for remediation of munition contaminated soil in a bioslurry reactor. Chemosphere. 40(4):441-8.
Hayes, T. D., D. G. Linz, D. V. Nakles, and A. P. Leuschner (Eds.). 1996. Management of manufactured gas plant sites, vol. 2. [p. 427-437: Chemical Oxidation]. Amherst Scientific Publishers, Amherst, Mass.
The combination of chemical oxidation and biodegradation of the present invention has the great advantage over either treatment alone in the remediation of organic contaminants: The use of Fenton""s reagent with biodegradation provides increased effectiveness in part because oxidized organic compounds (such as polyaromatic hydrocarbons, PAHs) are more water soluble than the original contaminants. The increased solubility leads to higher bioavailability and in turn the higher bioavailability results in more extensive remediation.
The inventors have discovered that oxidation methods for remediation of contaminates using transition metals and oxidizing agents accompanied by the introduction of a complexing or chelating agent for the transition metal can be conducted without the usual decrease in soil pH. This feature of pH maintenance provides several advantages. For example, the use of the complexing or chelating agent to modify Fenton""s reagent chemistry allows for the maintenance of pH at levels suitable to sustain bacteria and further permits microbial action to enhance the remediation process.
The advantages of maintaining biocompatible pH levels include the ability to contemporaneously obtain effective bioremediation by naturally occurring and/or introduced bacteria. Furthermore, use of a chelating agent eliminates the concern of an acidified soil environment which is associated with the original Fenton reaction. Among such complexing agents are included hydroxylated benzenes, which have been found to be especially useful. More desirably, dihydroxybenzene provides particularly desirable results.
The transition metals useful in practicing the present invention include manganese, iron, cobalt, nickel, copper and zinc, with iron salts being preferred, the iron salt preferably being a sulfate, a perhalate or a nitrate. More preferably the iron is a Fe(II) ferrous salt or a ferric Fe(III) salt, and most preferably as an Fe(III) ionic species. The Fe(III) may be a sulfate or a nitrate, but is preferably a perhalate, such as perchlorate, perbromate or periodate, with perchlorate being optimally preferred.
Oxidizing agents useful in the methods of the present invention may be any of a number of oxidizing agents that provide a reactive free radical in the presence of a transition metal:chelator complex at a pH in the neutral range. Among the useful oxidizing agents are peroxides such as for example, hydrogen peroxide, which is especially preferred.
The chelating agents useful in the present invention may be any chelating agent that forms a transition metal chelate with the transition metal chosen for production of the reactive oxidizing free radical. Hydroxylated aromatic compounds are especially useful as chelating agents in these methods. Examples of useful chelating agents include hydroquinone, orcinol, resorcinol, trihydroxybenzene, salicylate, m-hydroxybenzoate, p-hydroxybenzoate, nitrilotriacetic acid and diethylenetriaminepentaacetate. Preferred chelating agents for use in combination with iron as Fe(II) or Fe(III) as the transition metal include the hydroxybenzenes and the hydroxybenzoic acids. Optimally, the chelating agents for use in combination with Fe(II) or Fe(III) are catechol (1,2 dihydroxybenzene) or gallic acid (3,4,5 trihydroxybenzoic acid).
The chelators are generally used in amounts sufficient to chelate the amount of transition metal introduced into the contaminate system. Desirably the ratio of transition metal:chelator complex to oxidizing agent may be any ratio from about five parts peroxide to one part iron by weight to about twenty parts peroxide to one part iron by weight. Optimally, the ratio of peroxide to iron is about ten parts peroxide to one part iron by weight.
It is important to note that the optimal ratio of peroxide to iron by weight may be affected by the type of contaminate and the amounts and the chemical composition of the contaminants therein. This ratio may be routinely determined for each contaminate on a small scale and applied on the a larger scale to the remediation or decontamination project at hand.
Gallic acid is among the hydroxybenzene chelating agents especially useful in the methods of the present invention. Gallic acid may be produced from plant tannins by standard well known chemical processes. The Materia Medica gives the following list of plant genera (along with examples given their common names) that are high in tannins and which would therefore be of value as inexpensive sources of tannins for the production of hydroxybenzene chelating agents, particularly gallic acid: Abies (Spruce), Agrimonia (Agrimony), Alnus (Alder), Betula (Birch), Cinnamomum (Cinnamon), Cola nitida (Cola Nuts), Ephedra (Mormon Tea), Fraxinus (Ash), Geranium (Cranesbill, Alum Root), Granatum (Punica, Pomegranate), Guaiacum (Lignum Vitae), Hamamelis (Witch Hazel), Heuchera (American Alum Root), Juglans (Walnut, Butternut), Ligustrum (Privet), Myrica (Bayberry), Orobanche (Broomrape), Potentilla (all), Prunus (Wild or Choke Cherry), Quercus (Oak), Rheum (Rhubarb), Rhus (all: Sumach), Rosa (Rose), Rubus (Blackberry, Raspberry), Vaccinium (Blue-/Huckle-/Bilberry), Xanthium (Cocklebur).
Without wishing to be bound by any particular theory, it is believed that the presence of the chelating agent stabilizes the reactive transition metal ion in the complex and prevents precipitation as a ferric salt without inhibiting the catalytic activity of the transition metal ion. The transition metal ion in the complex interacts with the oxidizing agent in the reaction mixture enhancing the production of a highly reactive oxidizing free radical. The avoidance of the low pH prevents solubilization of heavy metals and enhances the biocompatibility of the reaction. The products of the remediation reaction formed when contaminates react with the highly reactive oxidizing free radical are also generally less toxic than the products of the commonly available harsher chemical remediation methods.
In addition to chemical treatment, the present invention provides combined chemical remediation and bioremediation techniques. Although naturally occurring microorganisms may be relied upon to perform degradative processes contemporaneously with the chemical treatment process of the present invention, it is desirable to select a consortium of microorganisms known to be effective at degrading the contaminants in the soil, and introducing such a consortium prior to, during or subsequent to such chemical treatment.
For example, a consortium known to be effective in degrading PAHs such as, a consortium of Burkholderia spp., Ochrobactrum spp., and Actinomyces spp. can be introduced into the soil, and permitted to contemporaneously work along with chemical oxidation treatment. In this way, the advantages of both chemical treatment and bioremediation can be obtained.
The invention also provides a kit for treatment of a contaminate contaminated with an organic compound, the kit includes: a transition metal in soluble form; a chelator of the transition metal that has the property of forming a transition metal:chelator complex with the transition metal; and a buffering salt that is soluble in acidic solutions. The buffering salt may have a pKa suitable to maintain the pH in the neutral range. Preferably the buffering salt has a pKa in the range from about 5 to about 8.
The transition metals and transition metal chelators useful in the kits of the present invention are as described above. The transition metal chelator is most preferably catechol or gallic acid. The kits preferably also contain an oxidizing agent that reacts with the transition metal:chelator complex to form a reactive free radical. The preferred oxidizing agent is hydrogen peroxide.
The kit may further comprise a microbial consortium having the property of solubilizing or biodegrading an organic compound contaminant. Preferably the microbial consortium comprises one or more of the following: a bacterial species, a fungal species and an actinomyces species. The bacterial species, a fungal species and an actinomyces species that are particularly useful in the kits of the invention have been described above. These include one or more of the following: an Alcaligenes species, a Sphingomonas species, a Pseudomonas species, a Rhodotorula species, a Burkholderia species, an Ochrobactrum species, a Rhodococcus species, a Xanthomonas species and an Actinomyces species.
The following examples were conducted to test the efficacy and sequence of combined chemical oxidation and biodegradation in the remediation of soils contaminated with a mixture of PAH compounds from the site of a former manufactured gas plant (MGP).